Referring firstly to FIG. 1 a resonator 1 is shown having a central conductor 1a and loop-coupled devices 2 and 3 engaged therewith. Co-axial lines 4 and 5 carry signals to and from loop devices 2 and 3. By rotating loops 6 and 7 the loaded Q of the resonator may be varied. Loops 6 and 7 are rotated in concert i.e., each loop being disposed at the same angle to a line passing through the centers of the loops to ensure that the correct impedance is obtained at both the input and output ports.
Referring now to FIGS. 2 and 3 a typical prior art loop-coupled device is shown. Connector 8 consists of a body portion 9 connected as its base to a mounting plate 10. A central conductor 11 is held co-axial with and electrically isolated from body 9 by insulating material 12. A loop 13 is electrically connected at one end to central conductor 11 of the connector and at the other end to mounting plate 10.
As can be seen in FIG. 3 the mounting plate 10 is provided with a number of elongate slots 14 around its periphery. The mounting plate 10 is fastened to the top wall 15 of a resonator by screws 16.
In use, the connector is placed within aperture 17 of wall 15, the screws are placed through the slots 14 and loosely screwed into wall 15. The connector may be rotated to achieve the desired loaded Q factor. When in the desired position screws 16 may be fastened to hold the connector in place and provide electrical contact.
This design has two major drawbacks. Firstly, the slots reduce the strength of the mounting plate 10 adjacent screws 16 and limit the degree of force that can be applied between mounting plate 10 and wall 15. This may result in a poor contact being formed between mounting plate 10 and wall 15, resulting in unwanted intermodulation frequencies. Further, connection and disconnection of connectors to connector 8 may result in rotation of the connector relative to wall 15, which may alter the loaded Q factor from its tuned value.
It is an object of the present invention to provide a coupling device which mitigates the above disadvantages or at least provide the public with a useful choice.